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Full text of "The Cambridge Natural History"

18                                  VESTIGIAL   POUCHES                               CHAP,
opens backwards is less disadvantageous to the contained
young.
The male Thylacine has a pouch which is quite or very
nearly as well formed as in the female. There are also rudi-
ments of a pouch in the male foetuses of many Marsupials,
especially of those belonging to the Polyprotodont section of the
order, though these rudiments are by no means confined to that
subdivision. Up to so late a period as the age of four months
(length 19*8 cm.) the male Dasyurus ursinus has a pouch.
We have now to consider the interesting series of facts
relative to the permanence—in a rudimentary condition it is
true—of the mammary pouch in the higher Mammalia, facts
which seem to be an additional proof that they have he.en
derived from an ancestor in which the pouch was an organ of
functional importance. The first definite proof of the occurrence
of a pouch in any mammal not a Marsupial or a Moiiotreine was
made by Malkmus, who found this structure in a Sheep. It
seems, however, that the structures found in the higher mammals
are not always comparable to the marsupmm of the Marsupials,
but sometimes to the mammary pouch of the Monotreme. That
the Marsupials are a side line, and not involved in the ancestry
of the Eutheria, is an opinion which is at present widely held. At
the same time it is reasonable to suppose that the original stock
lying between the Prototheria and the Metatheria, whence the
latter and the Eutheria have arisen, preserved both the mammary
pouch of the lower mammal and the marsupium of the further-
developed stage, as does Phalangista, occasionally at the present
day. Hence to find remnants of both structures in existing
mammals would not bo incredible. This is what Dr. Klaatsch
believes to be the case. In certain Ungulates, including two
species of Antelope, Dr. Klaatseh found very considerable rudi-
ments of folds provided with nnstriated muscular fibre; there
were in the adult Cervicapra isabellina a pair of pouches, one on
each side, and a rudiment of a second on either side; possibly
this multiplication of the pouches has relation to the number of
young. That there is more than one pouch makes a comparison
with the mammary pouch rather than with the marsupium
probable. The Ungulate teat, it must be remembered (see p. 16),
is a secondary teat; hence there is no difficulty in the com-
parison from this point of view. A pouch containing a primary